1. Field of the Invention
The present invention relates to a brake drum used for a drum brake of an automobile or motorcycle.
2. Description of the Related Art
As a brake drum, for example there is the one shown in Japanese Patent Publication (A) No. 2004-084889. Fine relief shapes are formed at the outer circumferential surface of the brake drum so as to increase the surface area and thereby improve the heat radiating ability and efficiently conduct heat generated at the brake drum from the fine relief shapes to a wheel hub.
As related art, there is Japanese Patent Publication (A) No. 2004-084889.
However, in the brake drum shown in Japanese Patent Publication (A) No. 2004-084889, fine relief shapes are formed at the outer circumferential surface, but shot blasting is used to form the relief shapes, so the drag strength in the rotational direction is not sufficient. Further, the rigidity in the diametrical direction is not sufficient, so sometimes the vibration caused by friction with the brake shoe causes abnormal noise.